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March 8, 1932. kfmcLfmcoLsoN 1,343,490

STRESS MEASURING Filed March 11. 1927 2 Sheets-Sheet l .colvsmvr mm. 45 4/ oscuuran l j I INVENTOR 20 v Amman menu mcuLsuN ATTORNEY March 8, 1 932.- A. M L. NICOLSON STRESS IEASURING Filed larch 11. 1927 2 Sheets-Sheet 2 INVENTOR' lLEXRNOER McLERN NICOLSON ATioRNEY Pat nted? 8,1932 v UNITED sures v PATENT m mxnimm HGT-IRAN K100115011, 0] NEW YORK, N. 'YQASSIGNOB, BY HESNE ASSIGN- mmrs, 1'0 mm TEIMBAPH COMPANY, A. CORPORATION OE CALIFORNIA Application filed latch 11, 1927. Serial I0. 174,489.

This invention relates to a method and apparatus for measuring and determining conditions ina physical medium such as tension, compression, or deformation resulting from 5 changes in load, changes of temperature, and

the like; and more particularly to such apparatus utilizing a plurality .of electrical oscillating circuits comprising piezo-electric crystal devices arranged to produce two sets of electrical oscillatlons which interact to produce a third set of beat frequency oscillations, the frequency of which is a determinable function of the condition to be measured, and by the measurement of which, the

unknown condition may be determined.

It is an object of this invention to rovide a method and apparatus which may e used to determine with a high degree of accuracy conditions which might otherwise be diificult 90 or impossible to measure or determine.

It is a further object of this invention to provide a method and apparatus for producin as a-function of the unknown condition tolie measured, two sets of electrical oscillations, one of which may be of constant frequency and controlled as to freguency by a piezo-electriccrystal device or evices, and the other of which may vary as a determinable function of the condition to be measured, 80 whereby beat frequency oscillations are produced by the interaction of the two sets of oscillations, the beat frequency. being a determinable function of thecondition to be measured; or for producing two sets of elec-- trical oscillations both of which may vary in the opposite sense as a determinable function of the condition to be measured, thereby producing beat frequencies which vary, as a different determinable function of the condition to be measured. It is still a further object of this invention to provide a method and apparatus for utilizing a piezo-electric device for establishing and controlling the frequency of both sets of oscillations whereby a very high degree of accuracy may be obtained in the determination or measurement of the condition to be determined or measured.

I attain these objects. by apparatus illustrated in the accompanying drawings in which-.

Fig. 1 is a circuit diagram showing a variable frequency oscillator.

Fig. 2 shows the application of my invention to the measurement of expansion and contraction in a member due to load or temperature changes.

Fig. 3 shows a modification in which oscillations may be generated at a plurality of freo0 quencies simultaneously.

Figs. 4 and 5 show arrangements adapted to convert the unknown conditions of measurement into forces afiecting the measuring means of my invention.

Fig. 6 shows a member, the stress conditions in which are to be measured.

' In my co-pending application, Serial No. 269,570, filed April 12, 1928 as a division of this application, certain features of my invention as herein disclosed have been claimed since they constitute divisional. subject matter.

' In accordance with one form of my invention, I provide a system for generating elec- '75 trical oscillations, the frequency of which depends upon the condition to be measured. In its preferred form, this apparatus comprise an amplifying system of the thermionic vacuum tube type having a piezo-electric crystal system coupling the output of the amplifier system to the input thereof. The piezo-electric crystal system preferably comprises a piezoelectric crystal connected in the output circuit of said amplifying sys- 85 tem and deriving energy therefrom; as will be understood, this crystal will vibrate mechanically in response to the impression of electrical oscillations thereon.

The above mentioned piezo-electric crystal device, which I may term the output crystal is mechanically coupled to a second crystal device connected in the input circuit of the amplifying system in such a manner as to commlmicate to the second crystal which I may term the put crysta the vibra? tions developed by t e output crystal. The mechanical couplin between the c stals for transmitting he vi rations from t 0 one tothe, other is such that a change in its physical I frequency at which the system oscillates.

. constant.

' der such conditions,

oscillations will be an indication,

condition, as for instance an increase or de-. crease in the tension or compression existing. therein, or a change in the distance between the input and output crystals, will cause a change of the 'mec anical tunin of the two crystals and thereby achange o the natural It will be understood by those familiar with the art that an amplifying system connectedas described will operate as a generator of electrical oscillations.

It will be understood that the device will be operated between such limits that the frequency of the oscillations generated is a determinable function of the condition to be measured.

' For the purpose of determining the frequency so generated, which may be far above I prothe limit of audibility in certain cases, vide a second oscillation generating system, also of the thermionic vacuum tube type, and comprising a piezo-electric crystal device for establishing and controlling the 7 frequency generated by the second system. The piezoelectric crystal device will be maintained undesired is such as to require it, that the piezoelectric crystal device fixing the frequency of the second oscillating system may be maintained at a constant temperature, pressure, and degree of humidity, to assure that the frequency of the second system is truly The oscillations produced by the first and second systems may be caused to interact to produce beat frequency'oscillations which may be selected and amplified and eventually detected; it will be understood that the frequency of these beat, frequency. or in other words, a determinable function of the unknown condition to be determined, and when the system is once calibrated, it will be pos-' sible to determine the unknown condition merely by tuning a selecting circuit such as a wave meter to the frequency'of the beat oscillations and noting the position of tlie tuning elements.

My invention lends itself readily to the de' termination of many unknown conditions: for example, al members may be determined, either within or beyond the elastic limit, and it ma be determined when such structural mem rs are begifloaded to a dangerous point. If desi relays may be provided, arranged-to operatici when the elastic limit s approached m sue of dangerous conditions. Temperatures may be determined at any desired time at points which ma fact, it beclear such a system lends itself measurement with tothe determination and P y i l.

a h degreeofa'ecuracypf many ums. In accordance with anotherv and'in some instead of utilizing between them, subject to variation,'as aif the degree of accuracy the loads in all sorts of structurmembers, thereby giving a warning. Potential Such as battery instances preferred form of my invention,

a pair of oscillating sysgenerates oscillationsof constant frequency andthe other oscillations of a frequency which is a determinable function of the condition to tems, one of which of different frebe measured, I may utilize a single amplifying system generating simultaneously oscillations quencies one of which inay be constant and the other of which may vary as a determinable and a piezo-electric crystal associatedwith the input circuit, and a mechanical coupling function of the condition to be measured..- The variation of the coupling, as previously pointed out, will cause a change in the natural frequency of each of the systems andthereby a change in the frequency of each-of the sets of oscillations.

If a force dependent upon the conditions function of the condition to be measured, or,

circuit coupled to its input circuit by'means to be measured, be applied tothese couplings, such that it has the opposite efiect in the two couplings, then the twofrequencies will vary in the opposite sense. For exalmple, if one of the couplings comprises a meniber. adapted to be compressed, while the other coupling comprises a niember ada'pted tobe placed under tension, in-accordance' 'with the unknown condition, which may be the cas'e'if the'two coupl'ings are arranged as cross members in a ring of'elastic material anddisposed at right angles to each other, then the frequencies generated by the system will vary inopposlte senseswhen the ring is subjected to compression or tension along the line of one of the cross members.

Referring now more particularly to Fig. 1,

1 designates a variable comprising an amplifying system 2 of the. thermionic vacuum'tube type diagrammatically shown'as a single vacuum tube device frequency oscillator comprising grid or control electrode 3, anode or plate 4, and cathode or filamentary cathode 5. A suitablecoil 6'is connected to the anode 4: on the one hand and to a suitable source of 7 on the other hand. The filament 5 isienergized by suitable source such. as battery 8 A piezoelectric c 'stal device 10 such for example as a crysbe relatively inaccessible. In '5 talofRochelle-salt'exhibiting'the fhour glass f configuration, a crystal of quartz or any other suitable crystal, is provided 'with electrodes 11 and 12 arranged'as may be desired,-eleetrade 11 being the tem, and electrode 12, being connected to the control electrode 3.

The crystal device 10 with its electrodes and 12 constitute the input crystal of the variable frequency oscillator 1. The output an intermediate point upon the coil 6.

It will be understood that proper adjustment of the point of connection of electrode 15 to coil 6 ahd of the various potentials and phase relations, will cause the generation of sustained oscillations, the frequency of which is a function ofthe natural period or periods of the crystals 13 and 11 and of the coupling therebetween. if the coupling is such as to vary under the control of the-unknown condi; tion to be determined, then the natural ffre quency at which the system will oscillate, will be a function of the unknown condition. Certain preferred forms and arrangements of the variable coupling will hereafter be described in more'detail.

The frequency of the oscillations generated by the system 1, may be one of a. wide range including audible frequencies and superaudible frequencies.

For convenience and accuracy in'the determination of the frequency-of the oscillations produced by the system 1, I preferably provide a second oscillation'generating. system 20 adapted to generate oscillations of a constant frequency, which may be sochosen as to interact with the oscillations produced by the system 1 to produce oscillations of audible beat frequency, which may be detected and readily measured as to pitch or frequency.

1F orthe-purpose of providing oscillations'of' the constant frequency required, I preferably provide a second vacuum tube amplifying system dia rammatically-shown as a vacuum tube ampli er 22 having a control electrode or grid 23, an anode or plate 24, and a filamentary cathode 25. Coil 26 is connected inthe output circuit asbefore, on the one hand to the plate 24;- and on the other hand to acoil 26. cc.

' suitable source such as battery 27 and the fila- 'ment is heated by a suitable source, such as battery 28.

A' piezo-electric crystal device 29 provided, having a common filament electrode 30, and a pair of separated electrodes 31 and 32. The electrode 31 is connected to the grid or control electrode 23 and the electrode 32- to a. suitable intermediate point upon the It will now be understood that by proper ad ustment of the variousconstants, the amp fy 'ng system 20 will generate sustained osclllation's of a frequency determined and t v controlled by the crystal device 29 and in order to assure that the frequency does-not vary, the crystal device may be maintained detector 37 may be provided having its control electrode 38 connected to one terminal of coil 35 and its'filament 40 connected to gthe other terminal thereof. The anode 39 may be connected through a suitablecoil 44 and a-suitable source of ipotential 42 to the filament circuit. The filament may be energized by suitable battery 43. A suitable coil 45 may be coupled to coil 44, and connected through tuning condenser 46 and suitable indicator such as telephone receivers 41 whereby 'the system may be tuned to the beat frequency, or It will be understood, however, that in place of the vacuum tube detector 37 a suitable crystal or other detector may be substituted.

It will now be clear that if the systems 1 and 20 be adjusted to produce oscillations which differ from each other by frequencies within the'range of audibility, then the fre-- quency' or itch of the beat frequency oscillations may e determined by tuning the circuit comprising coil 45 and condenser 46 toobtain the maximum response in the indicator 41; and if the frequency of the oscillations generated by system 1 varies as a result of the changes in the coupling 16, the pitch of the sary to tune the selection circuit and to observe the setting of the tuning elements. By

referring to the chart or curve the unknown condition may be determined.

Referring now more particularly to Fig. 2,

I have shown in detail, one form ofvariable coupling 16, as well as the use of the system for measuring expansion and contraction in a member, due to a load or temperature changes. In this instance, 50 designates a member to be observed: 51 and 52 respectively are top and bottom brackets clamped thereto and carrying crystal device 10 and 13 respectively. A suitable cup'53, which I term a top cup is secured to the under side of the beat frequency oscillations will change in a w crystal device 10, and a suitable cup 54, which I'term bottom cup is secured to the upper side of crystal device 13. The cups 53 and- 54 are so chosen and arranged as to fit one within the other, leaving a space between the bottom ofthe respective cups and also between the upturned edges. This space is partly filled with a suitable liquid such as mercury, oil, glycerine, gelatine, or the like, to a point such that the liquid extends up into the annular chamber between the upturned edges of the cups.

If now, the distance between the brackets 51 and 52 be changed as a result of tension or compression applied to the member 50, or as a result of temperature changes, the distance between the cups will be changed: the

distribution of the liquid will be changed, and a change will be caused in the natural freuency of the coupling 16, resulting in a c ange of the frequency of oscillations generated by the system 1, which may be measured and interpreted as already described.

Referring now'more particularly to Fig. 3, I have shown a modified form of my inven- .tion, in which a single vacuum tube amplifying system is arranged to generate oscillations of a plurality of frequencies simultaneously, the frequency of each group being caused to vary in the opposite sense as a function of the condition to be determined. In this instance, the oscillator comprises a thermionic vacuum tube amplifier 61, having control electrode 62, and filamentary cathode 64 energized by a suitable source of potential such as battery 65. A suitable source of potential 66 is connected to the anode 63, the other terminal of which is connected to a suitable coil 67, the other terminal of which is connected to the filament system. a The input circuit comprises coil 68 connected between the control electrode 62 and the filament 64. A series of coils 69, 7 O, 71 and 72 are provided, the coils 69 and 70 being coupled to coil 68, and the coils 71 and 72 being coupled to coil. 67. Coil 71 is arranged to deliver energy to electrodes 74 .and 75 of a suitable piezo-electric crystal device 73: as willibe understood, the piezo-electric crystal device will thereby be set into mechanical vibrations ata natural frequency depending upon the size, shape, and the coupling 79. The vibrations developed in the crystal device 73 are transmittedthrough the variable coupling 7 9 to crystal device 76 provided with electrodes 77 and 78 and'connected'to coil 70.

Thevibrations of the crystal device 76, as

1 will be understood, cause the production of 55 quency of which charges upon the electrodes 77 and 78, which are fed back to the input circuit of the amplifying system by the proper adjustment of the constants, continuous oscillations will be produced by the amplifying system, the freis determined by the conand material of the crystal device,

operation of the crystal device 88 causes the production of charges upon electrodes'89 and 90, which are transmitted to the coil 69 and thence to coil 68 into the amplifying system.

It will be understood that the system is thereby generating two sets or groups of oscillations imultaneously, the frequency of .each, set being a function of the corresponding piezo-electric crystal systems. If the variable couplings 79 and 91are both variable in the same sense as a function of the unknown condition, the fre uency of both sets of oscillations generate will likewise vary in the same sense. However, if the frequency of one coupling is caused to increase with the condition to be determined, .while the frequency of the other coupling is caused to decrease, the oscillation frequencies similarly change, and a relatively large 'chan e in beat frequency may be caused to appear y a relatively small change in the condition to be measured.

As is well understood in the art, the amplifying system 61, may, at the same time, operate as a detector without affecting the operation as a generator, as a result of which,

coil 92 may be provided inductively associated with coil 67 or with coil 68, and comprising in circuit therewith a tuning device such as a variable condenser 93 and an indicator such as telephone receivers 94, by means of which the frequency of the beat currents may be established.

Referring now more particularly to Figures 4 and 5, I have shownan arrangement .adapted to convert the unknown condition to be measured into forces affecting the variable couplings 79 and 91 in the opposite sense. There may be provided a suitable stress ring 100 of any suitable material such for example as steel. The ring 100 may be provided with a pair of cross members 101 and102' disposed at right angles to each other and secured in position within the ring in such manner that stresses applied thereto are transmitted to the cross members. It will be obvious that with a ring, the cross members will experience opposite stresses for a force applied to the ring in certain directions with reference to a cross member, providing the cross members enclose an angle which is not less than ap proximately forty-five degrees.

In the arrangement shown, crystal device 73, may be secured upon one side of the cross and 7 6 ction of I member similar to the member 50 o the conditions in which are to be measured. Apair of spaced brackets 106 and 107 are se-.

' It will coupling 91. If new,

placed under tension member 101, while crystal device 76 is secured upon the opposite side thereof. Similarly, crystal device 85 may be secured upon one side of the cross member 102 while crystal device 88 is secured upon the other side thereof. In this arrangement, the cross member 101 will then constitute the variable coupling 79, and the cross member 102 the variable compression be applied to the ring along the diameter of the cross member 101, said cross member will be placed under compression while the opposite cross member will be subjected to tension, as a result of the deformation of the ring 100 into the shape shown by the dotted lines, greatly exaggerated for the purpose. If on the other hand, the ring be subjected to tension along the diameter of the cross member 101, the

said cross member will be subjected to tension and the cross member 102 placed under compression: while, if the'force be applied along a line bisecting the angle between the said cross members, both will be caused to vary in the same sense, that is, both will be or compression.

Fig. 6, 105 desi ates a Referring now to Fig. 2,

curely fastened to the member 105 in the proper spaced relation to receive the ring 100. now be apparent "that if the ringis placed the position shown in Fig. 6 and secured therein, changes in spacing between the brackets 106 and 107 will cause stress variations in the opposite sense in the cross memhere 101 and 102, and thereby variations in the beat frequency produced by the system. By calibrating the apparatus, it will then be possible to determine very minute changes in the condition of the load, temperature, etc., in the member 105.

While I have shown and described certain preferred embodiments of my invention, "it

W111 be understood that modifications and changes may be made without departing from the spirit and scope thereof, as will be under! stood by those skilled in the claim '1. In a measuring member, two auxiliary measuring members,

pair of piezo-electric crystal elements hav--. ebetween. a g system for.

'oiifiuxifiary member, is subjected to compression the otherauxiliary member'will be subjected tension, means for applying each means for determining and means for measuring the tween the two frequencies of oscillations genand in such manner that system, a measuring said tube,

ofcross members attached to each of said pairs of piezo-electric crystals,

means for-producing beat frequency oscillations b interaction of the oscillations produced y the first. and second systems, and the frequency of the beat frequency oscillations.

2. In a measuring system, a measuring member, athermionic system for generating oscillations of two or more frequencies, comprising two pairs of piezo-electric crystal elements, circuits for controlling the frequencies of said oscillations by said piezo-electric crystal elements, means for applying each of said pairs to diiferent points on said measuring member in such manner that the crystals of each of said pairs are mechanically coupled by a portion of said measuring member,

difference beerated by said thermionic system.

3. In a measuring system, a measuring member, a thermionic system for generating oscillations of two or' more frequencies, comprising two pairs of piezo-electric crystal elements, circuits for controllin the frequencies of said oscillations by said piezo-electric crystal elements, means for applying each of said pairs to different points on ing member in such manner ithat the crystals of each of said pairs are mechanically coupled by a portion of said measuring member the natural frequency of one pair will be increased when said measuring member operates to decrease the natural frequency of said other pair, and means for measuring the difference between the two frequencies of oscillations generated by said thermionic system.

4 In a measu 7 g system, a measuring member, two auxiliary measuring members, a thermionic tube, input and output circuits for said tu ,means for feeding said output circuit back into said input circuit, a pair of a portion of one of said auxiliary easuring members, another pair of piezoelectric crystal elements mechanically coua thermionic amplifying system for-gener-j; a POI'tiOl1 9f the other of Said .ating, electrical oscillations,- comprising a lhary measuring members, electrical cir-' said measurpiezo-electric'crystal elements mechanically coupledby cuits for each of said crystals, means for electrically coupling the circuit of one crystal of each of said pairs to the input circuit of and means for electrically coupling the circuit of the other crystal of each of said pairs to the output circuit of said tube.

5. In, a measuring system, a ring, a pair comprising a pair of piezo-electric crystal said ring and elements attached to one of said cross members at se arate points thereof, a second thermionic tu system for gene ting electrical oscillations and comprising a pair of piezoelectric crystal elements attached to the other of said cross members at sepgrate points thereof means for producing at frequency oscillatlons by interaction 0 the oscillations produced by the first and second systems, and 10 means for determining the frequency-of the beat frequency oscillations.

' 6. In a measuring system, a ring, a. pair ofcross members attached to said ring an so positioned as to include an angle of not 5 less than forty-five degrees, a pair of piezoelectric crystal elements attached to each of said cross members at separate points thereof, and a thermionic generating system havone crystal of each of said pairs in elec- 20 trical relation with the input: circuit of said 'generating system, and airing. the other crystal of each of said pairs in electrical relation with the output circuit of said generating system.

25 Signed at New York city, in the county of 1 New York and State of New York, this tenth day of March, A. D. 1927. w

IcUZAR 1110015011. 

